[time-nuts] NTP to discipline Raspberry Pi

[James Peroulas]

I was hoping to measure the ppm error of a Raspberry Pi's crystal using an
NTP client running on the Pi itself. The NTP client reports a ppm
correction that I find to be consistently (measurements performed over
several days) off by about 10 ppm compared to what I measure using my GPS
calibrated frequency counter (HP5328). Specifically, the Pi reports a
required ppm correction of -33 ppm whereas I consistently measure a
required correction of -43 ppm on my frequency counter.

Any ideas on where I can look to track down the discrepancy? Perhaps the
timers on the RPi are configured incorrectly in the kernel? Or is this the
best I can expect from NTP? I would understand the situation if the NTP
reported correction drifted above and below -43ppm, but it seldom departs
from -33ppm by more than 1 or 2 ppm...

Thanks,
James

P.S. I apologize if this isn't time-nutty enough :) I only need about 1ppm
accuracy in my corrections :)

-- 
*Integrity is a binary state - either you have it or you don’t.* - John
Doerr